Magnetic resonance imaging data suggest a strong relationship between childbirth and structural pelvic floor injury, likely originating from stretch or crush of maternal tissues during the expulsive phase of labor. Our preliminary studies show that the pelvic floor muscle most vulnerable to injury is the striated pubococcygeal muscle (PCM); 11-20% of parous women demonstrate a muscle defect a year postpartum. Although several types of muscle or nerve injury might cause PCM abnormalities, the occurrence of these injury types have not been clarified. Serial MRI of the pelvic floor potentially offers the ability to observe PCM defects over time and differentiate: 1) neurogenic injury with delayed atrophic defect formation, 2) myogenic injury as in muscle tear, and 3) recoverable injury without lasting defect. The Aims of this study are to: AIM 1) demonstrate that each of the three hypothesized PCM types of injuries occur on serial MRI, and AIM 2) obtain pilot data to determine the sample size needed to demonstrate that the type of injury explains differences in muscle strength, pelvic organ support, and continence status observed at 6-months postpartum. We will recruit 20 primiparous women at increased risk for PCM injury from a delivery that involved forceps or vacuum, 3rd or 4th degree perineal tears, or long duration of the 2nd stage of labor. We will obtain MRIs at 2 weeks and 6 months postpartum and perform functional PCM testing at 6-months by quantifying PCM strength (by instrumented speculum), pelvic organ support (by pelvic organ prolapse quantification) and incontinence (by standard urodynamic and survey measures). Our short-term goals are to generate pilot data for an R01 application Aimed at testing the relationship between injury type and pelvic floor function. Our long-term goal is prevention and treatment of incontinence and prolapse, with care based on an improved understanding of the injury responsible for the pathology.